Drafts: when typing a message you can choose "Save". You can then retrieve your draft and continue writing by going to your User Control Panel -> Manage Drafts.

Subscribe Topic: at the bottom of each thread there is a "Subscribe Topic" link, if you click it an email will be sent to you when a new post is made. Unsubscribing can be done though the same link, or in your User Control Panel -> Manage subscriptions.